Copper-nickel-titanium alloy and process for making same



United States Patent 6 COPPER-NICKEL-TITANIUM ALLOY AND PROCESS FOR MAKING SAME James C. Holzwarth, Royal Oak, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Original application August 8, 1950, Serial No. 178,345, now Patent No. 2,720,459, dated October 11, 1955. Divided and this application October 7, 1952, Serial No. 313,580

6 Claims. (Cl. 75-459) This invention relates to a hardening alloy and to a process for forming the same. More particularly, the invention relates to a copper base alloy containing nickel and titanium which may be added to a zinc base alloy to improve its wear resistance. This is a divisional application of my copending patent application Serial Number 178,345, filed August 8, 1950, now Patent No. 2,720,459.

Zinc base alloys commercially used today for purposes such as drawing dies usually possess inadequate wear properties for many requirements. It is therefore a principal object of the present invention to overcome this deficiency by providing a hardening alloy which may be added to such zinc base alloys to provide the latter with greatly increased wear properties, good castability and homogeneity. These desirable characteristics are obtained in a zinc base alloy by the addition of a copper base intermediate alloy containing highly wear-resistant nickel and titanium particles of optimum size and distribution. In particular, I have found that a zinc base alloy which contains aluminum and also magnesium is especially benefited with respect to its wear resistance by the addition of such a hardener. The aluminum and copper serve to increase the tensile strength of the final alloy while the magnesium overcomes the corrosive infiuences of any impurities which may be present.

It is a further object of the present invention to provide an intermediate alloy of the type described above which may be added to a zinc base alloy to form a die alloy possessing a low melting point and uniform shrinkage. The low melting point eliminates the need for elaborate equipment in the alloying procedure, only a comparatively simple gasor oil-fired melting kettle being required. The property of uniform shrinkage permits the exact size of castings to be predetermined with precision, eliminating the necessity for extensive use of profiling machines. Accordingly, this alloy is ideally suited for drawing die use inasmuch as the entire processing of dies com posed of this alloy is comparatively simple, requiring a minimum of equipment and labor. Cost is further reduced by the fact that this alloy can be remelted many times, permitting the alloy in obsolete dies to be almost entirely recovered.

In addition, both alloys can be readily cast, and the diversity of forms into which the molten final alloy will flow make it a very desirable material for a variety of purposes. Furthermore, castings of the formed zinc base alloy can be produced comparatively quickly and are available for production use within a relatively short time.

The high wear resistance obtained in the final alloy is due to the presence of hard particles of nickel and titanium which are believed to be principally the intermetallic compound NisTi. Regardless of the exact chemical composition of the particles, their presence in the softer matrix material is responsible for the marked increase in wear resistance, particularly the type of wear experienced with dies in drawing and forming operations. Furthermore, these hard particles, which closely approximate the specific gravity of the zinc-rich melt, do not float so readily as do hardening particles formed by the addition of many other hardening agents. Hence the present invention results in a final Zinc base alloy which has proper particle distribution as well as optimum particle size, thereby possessing physical characteristics which satisfy all requirements for an outstanding tool alloy.

Commercially satisfactory results are obtained in accordance with my invention with a final zinc base alloy containing 2.0% to 5.0% aluminum, 0.5% to 5.0% copper, 0.16% to 3.0% nickel, 0.04% to 0.8% titanium, and the balance substantially all zinc. Moreover, the inclusion of 0.03% to 0.40% magnesium is beneficial to reduce the corrosive tendencies of impurities such as lead, cadmium, and tin. It will be understood, of course, that these alloys may also contain as other incidental impurities such elements as iron and silicon.

More specifically, I have obtained outstanding wear characteristics in a zinc base casting alloy comprising 3.0% to 5.0% aluminum, 2.0% to 3.5% copper, 0.10% to 0.30% magnesium, 1.0% to 2.5% nickel, 0.2% to 0.6% titanium and 88.0% to 93.0% zinc. For obtaining optimum castability and wear resistance properties, I prefer a final alloy consisting, by weight, of approximately 4.0% aluminum, 0.25% magnesium, 3.25% copper, 1.6% nickel, 0.5% titanium, and the balance zinc, except for incidental impurities.

Wear resistance, of course, is a function of both the size and distribution of the hard nickel-titanium particles. Since particle size and distribution are dependent on such factors as metal viscosity, solidification rate and methods of alloying, this invention also provides a preferred procedure for preparing the alloys to produce maximum wear resistance with minimum attrition. Although the desired compositions may be obtained by separately adding the nickel and titanium to the zinc-rich melt, I have found superior results are obtained by introducing these elements in the form of a copper-nickel-titanium alloy hardener. The hard constituent of nickel and titanium is believed to be formed in this hardener during its preparation. Therefore, in order to form long-wearing particles of suitable size, this hardener is preferably added to the zinc as a solid alloy, the copper-rich phase surrounding this constituent being subsequently dissolved away by the zinc, leaving the harder nickel-titanium particles suspended in the zinc alloy.

The desired alloy composition is preferably obtained by melting substantially pure zinc and, after elevating the temperature of molten zinc to a range between 950 F. and 1050 F., dissolving therein approximately. 50% of the aluminum to be added. This latter step inhibits drossing of the zinc at higher temperatures- After further raising the temperature of the melt to approximately 1100 F. to 1300 F., the required amounts of copper, nickel and titanium are added, in the form of a ternary hardening alloy in the solid state, as hereinbefore indicated. The elevated temperature should be maintained until this hardening alloy is entirely dissolved, the solution rate being increased by periodic agitation. After complete solution is accomplished, I have found it desirable to lower the temperature of the melt to between approximately 900 F. and 950 F. and to add the remaining 50% of the aluminum, the addition of which may be sufiiciently early to aid in this cooling process. A suitable flux, such as ammonium chloride, may then be added to remove any objectionable oxides, after which the magnesium is introduced by preferably submerging in suitable molds.

Although the aluminum could alternatively all be added either before or after the addition of the coppernickel-titanium hardener, the above alloying sequence has been. found to be most satisfactory.

In accordance with my invention, satisfactory results have been provided with a copper-nickel-titanium hardener having the following composition: 45% to 90% copper, 8.0% to 40% nickel, and 2.0% to titanium. However, to obtain optimum particle size I prefer to use a hardener which consists of 55% to 70% copper, to 35% nickel and 4.0% to 10% titanium.

It is to be noted that in these alloy compositions the ratio of nickel to titanium corresponds approximately to the inter-metallic compound NisTi. Therefore, for optimum homogeneity and wear properties the titanium content should thus be held within the range of approximately 15% to of the combined weight of nickel and titanium, about 22% being the percentage which appears to produce the most outstanding results. Accordingly, the hardening alloy which I found to be most satisfactory consisted of approximately 62% copper, 30% nickel and 8% titanium. These hardeners, when added to the zinc-rich melt in the proportions hereinbefore indicated, form nickel-titanium particles which preferably comprise 1.0% to 3.1% of the zinc base alloy.

Inasmuch as the hard particles of nickel and titanium are formed in the alloy hardener during its preparation, the alloy procedure of this hardener is of considerable importance in achieving optimum results. Melting of the hardener should be carried on under an atmosphere of a suitable inert gas, such as argon, to reduce the normal small loss of titanium due to oxidation. 1 have obtained most satisfactory melting and high titanium recovery using an induction furnace under an argon gas atmosphere.

Accordingly, this copper-nickel-titanium hardening alloy is preferably prepared by melting the copper and adding electrolytic nickel thereto. The alloy is subsequently preferably heated to a temperature between 2500 F. and 3000 F. and the melt blanketed with the argon atmosphere, the titanium then being added to the melt either as commercial nickel-titanium or commercially pure titanium. In the former case, of course, the initial addition of the nickel would have to be reduced accordingly to provide for the proper final nickel content. These additions are preferably made slowly to permit proper solution and to keep the melt from chilling excessively before casting, the casting temperature preferably being in the range of approximately 3000 F. to 3200F. in shapes which will dissolve most readily in the molten Zinc-rich alloy, I prefer to form castings having a high ratio of surface area to volume, such as flat plates or thin sheets.

Although the final alloy formed has been described as particularly suitable as a drawing die material, it also may be employed to considerable advantage in other applications in which high wear resistance, good castability and homogeneity are of importance.

It is to be understood that, while my invention has been described by means of certain specific examples, it is not to be limited thereby except as defined in the appended claims.

I claim:

1. A copper base alloy consisting essentially of about 4% to 10% titanium, 8% to 40% nickel, and the balance substantially all copper, the proportion of titanium to the combined amounts of nickel and titanium being in the range between about 15% and 30%, a substantial proportion of said nickel and titanium being present in the form of a hard network of NiaTi.

' 2. An intermediate alloy for introducing hard nickeltitanium particles to a zinc base alloy for imparting high wear resistance thereto, said intermediate alloy conlnasmuch as it is desirable to cast the metal 7 sisting essentially of about 55% to 70% copper, 20% to nickel and 4% to 10% titanium, said nickel and titanium being present principally in the form of a network of NlsTi, the proportion of titanium to the combined amounts of nickel and titanium being in the range between approximately 15% and 30%.

3. A process of forming a copper base alloy which comprises melting copper, dissolving nickel and titanium in the molten copper, the melt being blanketed with an inert atmosphere during the addition of titanium and being at a temperature of at least approximately 2500 F. subsequent to said addition, said nickel and titanium being used in amounts sufiicient to constitute about 8% to and 4% to 10%, respectively, of the melt, the proportion of titanium to the combined amounts of nickel and titanium being in the range between approximately 15% and 30% to provide a network of NiaTi in the solidified copper base alloy, and thereafter casting the molten alloy.

4. A process for forming a copper base alloy, said process comprising melting copper and nickel together, dissolving titanium in the melt under an inert atmosphere, said nickel and titanium being used in amounts sufiicient to constitute approximately 8% to 40% and 4% to 10%, respectively, of the melt, the proportion of titanium to the combined amounts of nickel and titanium being in the range between 15% and 30%, superheating said melt to a temperature between 2500 F. and 3200 F., and thereafter casting the molten alloy.

5. A process of forming a copper base alloy which comprises melting copper and nickel together, blanketing the resultant melt with an inert atmosphere and thereafter dissolving a sufiicient amount of titanium in said melt under said inert atmosphere to form upon solidification 21 network of hard NiaTi in the copper base alloy, said nickel and titanium being used in amounts sufiicient to provide an alloy composition consisting essentially of about to copper, 20% to 35% nickel and 4% to 10% titanium in which the proportion of titanium to the combined amounts of nickel and titanium is in the range between approximately 15% and 30%, the resultant melt being superheated to at least 2500 F. after the titanium addition, and subsequently casting said melt.

6. A process of forming an intermediate copper base alloy for introducing hard nickel-titanium particles to a zinc base alloy to impart high wear resistance thereto, said process comprising melting copper and dissolving a quantity of nickel therein, blanketing the melt with an inert atmosphere and thereafter dissolving nickeltitanium in the melt, said nickel and nickel-titanium being added in amounts to cause the nickel and titanium to constitute about 8% to 40% and 4% to 10%, respectively, of the melt, the proportion of titanium to the combined amounts of nickel and titanium being in the range between approximately 15 and 30% to provide a network of NiaTi in the solidified copper base alloy, superheating the molten alloy thus formed to a temperature of at least 2500 F., and thereafter casting said alloy.

References Cited in the file of this patent UNITED STATES PATENTS 1,364,654 Tedesco Jan. 4, 1921 1,540,006 Hodson June 2, 1925 2,013,870 Starmann Sept. 10, 1935 2,102,238 Pilling et al. Dec. 14, 1937 2,156,348 Muller et a1. May 2, 1939 2,163,224 Alexander June 20, 1939 2,222,157 Ruzicka Nov. 19, 1940 2,317,179 Daesen Apr. 20, 1943 FOREIGN PATENTS 182,122 Great Britain May 24, 1923 362,507 Great Britain Dec. 7, 1931 

1. A COPPER BASE ALLOY CONSISTING ESSENTIALLY OF ABOUT 4% TO 10% TITANIUM, 8% TO 40% NICKEL, AND THE BALANCE SUBSTANTIALLY ALL COPPER, THE PROPORTION OF TITANIUM TO THE COMBINED AMOUNTS OF NICKEL AND TITANIUM BEING IN THE RANGE BETWEEN ABOUT 15% AND 30%, A SUBSTANTIAL PROPORTION OF SAID NICKEL AND TITANIUM BEING PRESENT IN THE FORM OF A HARD NETWORK OF NI3TI. 